An electrophotography-based image forming device such as a laser printer electrostatically feeds developer, such as toner, on an electrostatic latent image formed on a photosensitive member to develop a toner image. The toner image is transferred to a recording medium (for example, a sheet) to form an image. The developer is contained in a developer container (case) of a developing device and provided for development to a developing roller, such as a developing roller, rotatably supported at a predetermined position along an opening of the developer container.
When the developer contained in the developer container is leaked out from the developer container, the developer scatters to stain the interior of the image forming device and the recording medium. In order to prevent the leakage of developer as described above, for example, JP-A-2001-134080 discloses an image forming device including developer leakage preventing members called side seals respectively disposed at portions, where the longitudinal end portions of the developing roller oppose the developer container. The developer leakage preventing members prevent the leakage of the developer. The substrate of the side seal is made of an elastic material, such as urethane sponge. Since the developing roller is attached so as to press the side seal, the longitudinal end portions of the developing roller strongly contact with the side seals, respectively. Therefore, even when the developing roller rotates, the toner is prevented from leaking from the longitudinal end portions of the developing roller.
The side seal 109 (refer to FIG. 13B) is made of an elastic material such as urethane sponge and has a certain thickness so that when a developing roller 22 is attached to a case 21 of a developing cartridge 4, the side seal 109 is compressed and exerts a predetermined pressing force to the developing roller 22. When the developing roller 22 is attached to the case 21 of the developing cartridge 4, such a method is employed that a shaft of the developing roller is inserted into a supporting hole 21d formed on a case side portion 21a of the developing cartridge 4 and the developing roller 22 is placed on a side seal 109.
However, since the side seal 109 is, as described above, made of an elastic material having a certain thickness, a direction to which the side seal 109 is pressed and forcibly deformed is varied depending on how the developing roller 22 presses the side seal 109. Specifically, a shape of the side seal 109 at the time when the developing roller 22 is attached is very difficult to control with collapse of the side seal 109 taken into account. As one example shown in FIG. 13B, when the developing roller 22 is attached so as to press down the side seal 109 downward (in a direction apart from a blade 26), a large clearance 100 is formed in the vicinity of an upper end side 109e of the side seal 109. Then, the developer leaks from the clearance 100 and the developer scatters inside an image forming device.